The Tree View

Tree View Fundamentals

Introduction

Like a real world tree, the branches or nodes of a tree view use a type of relationship so that they are not completely independent. For example, a tree view can be based on a list that has a parent item and other child items that depend on that parent. In real world, if you cut a branch, the branches and leaves attached to it also disappear. This scenario is also valid for a tree view.

Most of the time, a tree has only one root but a tree in an application can have more than one root.

In a Windows application a tree view is primarily a control like any other. To use it in your application, you can click the TreeView button in the Toolbox and click a form or other control in your application. This is equivalent to programmatically declaring a variable of type TreeView, using the new operator to instantiate it and adding it to its container's list of controls through a call to the Controls.Add() method. Here is an example:

Imports System.Drawing
Imports System.Windows.Forms

Module Exercise

    Public Class Starter
        Inherits Form

        Private tvwCountries As TreeView

        Dim components As System.ComponentModel.Container

        Public Sub New()
            InitializeComponent()
        End Sub

        Public Sub InitializeComponent()

            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Controls.Add(tvwCountries)
        End Sub

    End Class

    Function Main() As Integer

        Dim frmStart As Starter = New Starter

        Application.Run(frmStart)

        Return 0
    End Function

End Module

This would produce:

Using a TreeView variable only adds a rectangular empty control to your application. The next action you probably take is to add one or more branches to the tree.

1. Start Microsoft Visual Basic
2. Create a new Windows Application named CollegeParkAutoParts2
3. In the Solution Explorer, right-click Form1.vb and click Rename
4. Type Central.vb and press Enter
5. From the Containers section of the Toolbox, click Panel and click the form
6. Set its Dock property to Top
7. From the Containers section of the Toolbox, click Panel and click the form
8. Set its Dock property to Bottom
9. From the Containers section of the Toolbox, click SplitContainer and click the middle of the form
10. Design the form as follows:
     

    Control Text Name Other Properties Label College Park Auto-Parts   BorderStyle: FixedSingle Font: Times New Roman, 20.25pt, style=Bold AutoSize: False TextAlign: MiddleCenter GroupBox     Anchor: Top, Bottom, Left, Right TreeView   tvwAutoParts Anchor: Top, Bottom, Left, Right GroupBox     Anchor: Top, Bottom, Left, Right ListView   lvwAutoParts View: Details Anchor: Top, Bottom, Left, Right Columns   (Name) Text TextAlign Width colPartNumber Part #     colPartName Part Name   300 colUnitPrice Unit Price Right 80 GroupBox Selected Parts     Label Part #   Anchor: Bottom, Left Label Part Name   Anchor: Bottom, Left, Right Label Unit Price   Anchor: Bottom, Right Label Qty   Anchor: Bottom, Right Label Sub Total   Anchor: Bottom, Right TextBox   txtPartNumber1 Anchor: Bottom, Left TextBox   txtPartName1 Anchor: Bottom, Left, Right TextBox 0.00 txtUnitPrice1 TextAlign: Right Anchor: Bottom, Right TextBox 0 txtQuantity1 TextAlign: Right Anchor: Bottom, Right TextBox 0.00 txtSubTotal1 TextAlign: Right Anchor: Bottom, Right Button Remove btnRemove1 Anchor: Bottom, Right TextBox   txtPartNumber2 Anchor: Bottom, Left TextBox   txtPartName2 Anchor: Bottom, Left, Right TextBox 0.00 txtUnitPrice2 TextAlign: Right Anchor: Bottom, Right TextBox 0 txtQuantity2 TextAlign: Right Anchor: Bottom, Right TextBox 0.00 txtSubTotal2 TextAlign: Right Anchor: Bottom, Right Button Remove btnRemove2 Anchor: Bottom, Right TextBox   txtPartNumber3 Anchor: Bottom, Left TextBox   txtPartName3 Anchor: Bottom, Left, Right TextBox 0.00 txtUnitPrice3 TextAlign: Right Anchor: Bottom, Right TextBox 0 txtQuantity3 TextAlign: Right Anchor: Bottom, Right TextBox 0.00 txtSubTotal3 TextAlign: Right Anchor: Bottom, Right Button Remove btnRemove3 Anchor: Bottom, Right TextBox   txtPartNumber4 Anchor: Bottom, Left TextBox   txtPartName4 Anchor: Bottom, Left, Right TextBox 0.00 txtUnitPrice4 TextAlign: Right Anchor: Bottom, Right TextBox 0 txtQuantity4 TextAlign: Right Anchor: Bottom, Right TextBox 0.00 txtSubTotal4 TextAlign: Right Anchor: Bottom, Right Button Remove btnRemove4 Anchor: Bottom, Right TextBox   txtPartNumber5 Anchor: Bottom, Left TextBox   txtPartName5 Anchor: Bottom, Left, Right TextBox 0.00 txtUnitPrice5 TextAlign: Right Anchor: Bottom, Right TextBox 0 txtQuantity5 TextAlign: Right Anchor: Bottom, Right TextBox 0.00 txtSubTotal5 TextAlign: Right Anchor: Bottom, Right Button Remove btnRemove5 Anchor: Bottom, Right TextBox   txtPartNumber6 Anchor: Bottom, Left TextBox   txtPartName6 Anchor: Bottom, Left, Right TextBox 0.00 txtUnitPrice6 TextAlign: Right Anchor: Bottom, Right TextBox 0 txtQuantity6 TextAlign: Right Anchor: Bottom, Right TextBox 0.00 txtSubTotal6 TextAlign: Right Anchor: Bottom, Right Button Remove btnRemove6 Anchor: Bottom, Right GroupBox Order Summary   Anchor: Top, Bottom, Left, Right Label Total Order:   Anchor: Bottom, Right TextBox 0.00 txtTotalOrder Anchor: Bottom, Right Button Close btnClose Anchor: Bottom, Right

11. Execute the application to test it
12. Close the form and return to your programming environment

To create the nodes of a tree view, Microsoft Visual Studio provides a convenient dialog box you can use at design time. To display it, after adding a tree view control to a form, you can click the ellipsis button of its Nodes field in the Properties window. This would open the TreeNode Editor:

The primary characteristic of a node is the text it displays. At design time and in the TreeNode Editor, to create a node, you can click the Add Root button. When you do this, a node with a default but incremental name is created. To edit a node's name, first select it in the Select Node To Edit list, then, on the right side, click Name and enter the string you wish.

The branches of a tree view are stored in a property called Nodes. The Nodes property is an object based on the TreeNodeCollection class. The TreeNodeCollection class implements the IList, the ICollection, and the IEnumerable interfaces.

As its name indicates, the Nodes property carries all of the branches of a tree view. This means that the Nodes property in fact represents a collection. Each member of this collection is called a node and it is an object based on the TreeNode class.

At run time, to create a new node, call the TreeNodeCollection.Add() method which is overloaded with two versions. One of the versions of this method uses the following syntax:

Public Overridable Function Add(text As String) As TreeNode

This method takes as argument the string that the branch will display. This method is also the prime candidate to create a root node. Here is an example of calling it:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.Nodes.Add("World")

            Controls.Add(tvwCountries)
End Sub

This would produce:

1. Right-click the form and click View Code
2. In the Class Name combo box, select (Central Events)
3. In the Method Name combo box, select Load and implement the event as follows:
    

   Private Sub Central_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Me.Load Dim nodRoot As TreeNode = tvwAutoParts.Nodes.Add("College Park Auto-Parts") For i As Integer = Date.Today.Year To 1960 Step -1 nodRoot.Nodes.Add(i) Next End Sub

4. Execute the application to test the form
    
   
5. Close the form and return to your programming environment
6. On the main menu, click Project -> Add Class...
7. Set the name to PartDescription and press Enter
8. To create a class that can holds a structured item of a list, change the class as follows:
    

   Public Class PartDescription ' These members will be used to define a car part Private ID As Long Private yr As Integer Private mk As String Private mdl As String Private cat As String Private name As String Private price As Double Public Sub New() ID = 0 yr = 1960 mk = "" mdl = "" name = "Unknown" price = 0.0 End Sub Public Sub New(ByVal code As Long, ByVal year As Integer, _ ByVal make As String, ByVal model As String, _ ByVal type As String, ByVal desc As String, _ ByVal UPrice As Double) ID = code yr = year mk = make mdl = model cat = type name = desc price = UPrice End Sub Public Property PartNumber() As Long Get Return ID End Get Set(ByVal value As Long) ID = value End Set End Property Public Property CarYear() As Integer Get Return yr End Get Set(ByVal value As Integer) yr = value End Set End Property Public Property Make() As String Get Return mk End Get Set(ByVal value As String) mk = value End Set End Property Public Property Model() As String Get Return mdl End Get Set(ByVal value As String) mdl = value End Set End Property Public Property Category() As String Get Return cat End Get Set(ByVal value As String) cat = value End Set End Property Public Property PartName() As String Get Return name End Get Set(ByVal value As String) name = value End Set End Property Public Property UnitPrice() As Double Get Return price End Get Set(ByVal value As Double) price = value End Set End Property Public Overrides Function ToString() As String Return PartNumber & " " & _ CarYear.ToString() & " " & _ Make & " " & _ Model & " " & _ Category & " " & _ PartName & " " & _ UnitPrice End Function End Class

The other version of the TreeNodeCollection.Add() method uses the following syntax:

Public Overridable Function Add(node As TreeNode) As Integer

This method takes as argument a TreeNode object. In other words, it expects a complete or semi-complete branch already defined somehow.

The TreeNode class is equipped with various constructors you can use to instantiate it. Its default constructor allows you to create a node without primarily giving its details. Another TreeNode constructor has the following syntax:

Public Sub New(text As String)

This constructor takes as argument the string that the node will display. Here is an example of using it and adding its newly create node to the tree view:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodElement As TreeNode = New TreeNode("World")
            tvwCountries.Nodes.Add(nodElement)

            Controls.Add(tvwCountries)
End Sub

We mentioned that the primary characteristic of a node is the text it displays. The text of a node is stored in a property of the TreeNode class and is called Text. This allows you either to specify the string of a node or to retrieve it when needed. Here is an example of setting it:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodElement As TreeNode = New TreeNode
            nodElement.Text = "World"
            tvwCountries.Nodes.Add(nodElement)

            Controls.Add(tvwCountries)
End Sub

Just as we called the TreeNodeCollection.Add() method to create a branch, you can call it as many times as necessary to create additional branches. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.Nodes.Add("World")
            tvwCountries.Nodes.Add("Jupiter")
            tvwCountries.Nodes.Add("Neptune")
            tvwCountries.Nodes.Add("Uranus")

            Controls.Add(tvwCountries)
End Sub

This would produce:

Alternatively, if you have many branches to add to the tree, you can first create them as an array of TreeNode values, then called the TreeNodeCollection.AddRange() method. The syntax of this method is:

public virtual void AddRange(TreeNode() nodes)

This method takes as argument an array of TreeNode objects. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodPlanets() As TreeNode = _
            { _
                New TreeNode("World"), _
                New TreeNode("Jupiter"), _
                New TreeNode("Neptune"), _
                New TreeNode("Uranus") _
            }
            tvwCountries.Nodes.AddRange(nodPlanets)

            Controls.Add(tvwCountries)
End Sub

At design time and in the TreeNode Editor, to create a child node for an existing item, first select it in the Select Node To Edit list, then click the Add Child button. This causes a child node to be created for the selected item. To edit its name, first click it and change the string in the Label text box.

At run time, to create a child node, first get a reference to the node that will be used as its parent. One way you can get this reference is to obtain the returned value of the first version of the TreeNodeCollection.Add() method. As its syntax indicates, this method returns a TreeNode object.

We have used the default constructor of the TreeNode class and the constructor that takes as argument a string. The TreeNode class provides another constructor whose syntax is:

Public Sub New(text As String, children As TreeNode())

The first argument of this method is the string that the new node this constructor creates will display. The second argument is a collection of the child nodes of this branch. The collection is passed as an array. Based on this, you use this constructor to create a new node including its children. After creating the new node, you can pass it to the TreeNodeCollection.Add() method as we did earlier. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = _
            { _
                New TreeNode("Africa"), _
                New TreeNode("America"), _
                New TreeNode("Asia"), _
                New TreeNode("Europe") _
            }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            Controls.Add(tvwCountries)
End Sub

This would produce

Using the same approach, you can create as many branches and their child nodes as you wish. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            ' Create a list of some African countries and 
            ' store them in an array named nodAfricans
            Dim nodAfricans() As TreeNode = _
            { _
                New TreeNode("Senegal"), _
                New TreeNode("Botswana"), _
                New TreeNode("Ghana"), _
                New TreeNode("Morocco") _
            }

            ' Create a list of some American countries and 
            ' store them in an array named nodAmericans
            Dim nodAmericans() As TreeNode = _
            { _
                New TreeNode("Canada"), _
                New TreeNode("Jamaica"), _
                New TreeNode("Colombia") _
            }

            ' Create a list of some European countries and 
            ' store them in an array named nodEuropeans
            Dim nodEuropeans() As TreeNode = _
            { _
                New TreeNode("Italy"), _
                New TreeNode("Greece"), _
                New TreeNode("Spain"), _
                New TreeNode("England") _
            }

            ' Create a list of continents, independently
            Dim nodAfrica As TreeNode = New TreeNode("Africa", nodAfricans)
            Dim nodAmerica As TreeNode = New TreeNode("America", nodAmericans)
            Dim nodAsia As TreeNode = New TreeNode("Asia")
            Dim nodEurope As TreeNode = New TreeNode("Europe", nodEuropeans)

            ' Store the list of continents in an array named nodContinents
            Dim nodContinents() As TreeNode = _
            {nodAfrica, nodAmerica, nodAsia, nodEurope}

            ' Create a branch named nodWorld and store the list of
            ' continents as its child
            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)

            ' Finally, add the nodWorld branch to the tree view
            tvwCountries.Nodes.Add(nodWorld)

            Controls.Add(tvwCountries)
End Sub

This would produce:

1. Access the Central.vb code file and change it as follows:
    

   Private parts(55) As PartDescription Private Sub Central_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Me.Load Dim nodRoot As TreeNode = tvwAutoParts.Nodes.Add("College Park Auto-Parts") ' This is simply used to initialize the whole array with empty parts ' This is just to make sure that each member of the array is defined For i As Integer = Date.Today.Year To 1960 Step -1 nodRoot.Nodes.Add(i) Next parts(0) = New PartDescription(447093, 2002, "Ford", _ "Escort SE L4 2.0", "Engine Electrical", _ "Alternator 75amp Remanufactured; w/ 75 Amp", _ 205.05) parts(1) = New PartDescription(203815, 2006, "Dodge", _ "Caravan SE L4 2.4", "Cooling System", _ "Radiator Cap", 6.65) parts(2) = New PartDescription(293047, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Thermostat Gasket", 4.95) parts(3) = New PartDescription(990468, 2002, "Honda", _ "Civic 1.7 EX 4DR", "Exhaust", _ "Bolt & Spring Kit (Manifold outlet, Muffler Inlet)", _ 85.75) parts(4) = New PartDescription(304158, 1996, "Buick", _ "Regal Custom V6 3.8", "Fuel Injection", _ "Fuel Injector", 82.75) parts(5) = New PartDescription(807245, 2004, "Acura", _ "MDX 3.5 4WD", "Driveshaft & Axle", _ "CV Boot Clamp 7 x 750mm; 1 Large + 1 Small Clamp", _ 1.6) parts(6) = New PartDescription(203485, 2001, "Ford", _ "Taurus LX V6 3.0", "Fuel Injection", _ "Oxygen Sensor OE Style 4Wire; Front; 2 Required", _ 52.65) parts(7) = New PartDescription(248759, 1999, "Jeep", _ "Wrangler Sahara", "Air Intake", _ "Air Filter AirSoft Panel", 7.95) parts(8) = New PartDescription(202848, 1998, "Honda", _ "Accord 2.3 LX 4DR", "Air Intake", _ "Air Filter", 12.55) parts(10) = New PartDescription(932759, 2006, "Kia", _ "Rio 1.6DOHC16V 4-DR", "Cooling System", _ "Thermostat", 14.45) parts(11) = New PartDescription(304975, 2000, "Honda", _ "Civic 1.6 EX 4DR", "Suspension", _ "Ball Joint; Front Lower; 2 per car", 40.55) parts(12) = New PartDescription(208450, 2003, "Chevrolet", _ "Monte Carlo LS V6 3.4", "Fuel Injection", _ "Oxygen Sensor OE connector; Rear", 65.55) parts(13) = New PartDescription(209480, 2002, "Ford", _ "Focus SE DOHC L4 2.0", "Steering", _ "Steering Rack Remanufactured", 170.85) parts(9) = New PartDescription(203495, 2004, "Honda", _ "Civic 1.7 EX 4DR", "Climate Control", _ "A/C Clutch; OE compressor = Sanden", 184.95) parts(14) = New PartDescription(203480, 2007, "Toyota", _ "Corolla", "Air Intake", _ "Air Filter", 12.65) parts(15) = New PartDescription(109379, 2005, "Volvo", _ "S40 2.5L T5 AWD", "Fuel Delivery", _ "Fuel Filter; Early Design; Outer Diameter = 55mm", _ 30.95) parts(16) = New PartDescription(935794, 2002, "Ford", _ "Escape XLS 4WD", "Brake", _ "Brake Caliper Remanufactured; Front Right", _ 65.55) parts(17) = New PartDescription(203485, 2006, "BMW", _ "325i", "Climate Control", _ "AC High Pressure Side Switch", _ 49.95) parts(18) = New PartDescription(204875, 1996, "Chevrolet", _ "Monte Carlo Z34 V6 3.4", "Fuel Delivery", _ "Fuel Filter", 8.05) parts(19) = New PartDescription(937485, 2007, "Toyota", _ "Camry V6", "Air Intake", "Air Filter", 12.95) parts(20) = New PartDescription(294759, 2001, "Ford", _ "Escape XLT 4WD", "Air Intake", _ "Air Filter Panel", 7.25) parts(21) = New PartDescription(297495, 2003, "Honda", _ "Civic 1.7 EX 4DR", "Brake", _ "Brake Caliper Reman; w/ ProAct Pads; Front Right", _ 82.55) parts(22) = New PartDescription(794735, 2006, "BMW", _ "325i", "Climate Control", _ "Cabin Air/Pollen Filter; With Activated Carbon", _ 28.05) parts(23) = New PartDescription(937485, 2007, "Toyota", _ "Corolla", "Body Electrical", _ "Halogen SilverStar; 12V 65W; inner-high beam", _ 22.85) parts(24) = New PartDescription(492745, 2005, "Ford", _ "Focus ZX3 L4 2.0", "Air Intake", _ "Fuel Injection Perf Kit", 342.95) parts(25) = New PartDescription(937005, 2004, "Acura", _ "MDX 3.5 4WD", "Driveshaft & Axle", _ "CV Boot Clamp 7 x 750mm; For Large End of Boot; inner boot", _ 1.6) parts(26) = New PartDescription(293749, 2004, "Acura", _ "MDX 3.5 4WD", "Driveshaft & Axle", _ "Axle Nut 24mm x 1;5; rear ", 2.35) parts(27) = New PartDescription(920495, 2006, "BMW", _ "325i", "Climate Control", _ "Adjustable Telescoping Mirror", 7.95) parts(28) = New PartDescription(204075, 2004, "Acura", _ "MDX 3.5 4WD", "Driveshaft & Axle", _ "Wheel Bearing; Rear; 1 per wheel", 70.15) parts(29) = New PartDescription(979304, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Thermostat Housing", 20.95) parts(30) = New PartDescription(300456, 2004, "Acura", _ "MDX 3.5 4WD", "Driveshaft & Axle", _ "Wheel Bearing; Front; 1 per wheel", _ 66.65) parts(31) = New PartDescription(404860, 2001, "Ford", _ "Taurus LX V6 3.0", "Suspension", _ "Shock Absorber GR2; Rear; Wagon only", _ 39.4) parts(32) = New PartDescription(585688, 2007, "Buick", _ "Lacrosse CXS V6 3.6", "Brake", _ "Climate Control", 10.65) parts(33) = New PartDescription(739759, 2001, "Ford", _ "Taurus LX V6 3.0", "Suspension", _ "Shock Absorber GasaJust; Rear; Wagon only", _ 30.95) parts(34) = New PartDescription(927495, 2005, "Volvo", _ "S40 2.5L T5 AWD", "Engine Mechanical", _ "Timing Belt Idler Pulley Original Equipment INA", _ 65.55) parts(40) = New PartDescription(979374, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Thermostat Gasket", 4.95) parts(35) = New PartDescription(542347, 2007, "Buick", _ "Lacrosse CXS V6 3.6", "Brake", _ "Brake Pad Set ProACT Ceramic w/Shims; Front", 80.05) parts(36) = New PartDescription(683064, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Radiator Hose; Upper", 103.75) parts(37) = New PartDescription(248759, 1999, "Jeep", _ "Wrangler Sahara", "Air Intake", _ "Air Filter", 50.95) parts(38) = New PartDescription(973974, 2007, "Toyota", _ "Corolla", "Air Intake", _ "Air Mass Meter; W/o Housing; Meter/sensor only", _ 134.95) parts(39) = New PartDescription(285800, 2001, "Ford", _ "Escape XLT 4WD", "Transmission", _ "AT Filter", 34.95) parts(41) = New PartDescription(207495, 2007, "Toyota", _ "Corolla", "Body Electrical", _ "Headlight Bulb; 12V 65W; inner-high beam", 9.35) parts(42) = New PartDescription(566676, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Auxiliary Fan Switch", 42.95) parts(43) = New PartDescription(304950, 2007, "Toyota", _ "Corolla", "Body Electrical", _ "Headlight Bulb; 12V 51W; outer", 7.85) parts(44) = New PartDescription(797394, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Water Flange Gasket", 0.85) parts(45) = New PartDescription(910203, 2007, "Buick", _ "Lacrosse CXS V6 3.6", "Suspension", _ "Strut Mount Inc; Sleeve; Rear Right", 80.85) parts(46) = New PartDescription(790794, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Radiator Hose; Lower", 9.45) parts(47) = New PartDescription(970394, 2007, "Buick", _ "Lacrosse CXS V6 3.6", "Suspension", _ "Coil Spring Insulator; Front Lower", 14.55) parts(48) = New PartDescription(290840, 2005, "Volvo", _ "S40 2.5L T5 AWD", "Engine Mechanical", _ "Rod Bearing Set 1 per Rod; Standard; Reqs. 5-per Engine", _ 26.95) parts(49) = New PartDescription(209704, 2007, "Toyota", _ "Corolla", "Body Electrical", _ "Wiper Blade Excel+; Front Right", 7.25) parts(50) = New PartDescription(200368, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Radiator Drain Plug incl; gasket", 3.15) parts(51) = New PartDescription(200970, 2005, "Volvo", _ "S40 2.5L T5 AWD", "Engine Mechanical", _ "Reference Sensor; Flywheel Engine Speed", _ 62.05) parts(52) = New PartDescription(542347, 2007, "Buick", _ "Lacrosse CXS V6 3.6", "Air Intake", _ "Air Filter", 50.25) parts(53) = New PartDescription(927045, 2001, "Ford", _ "Escape XLT 4WD", "Air Intake", _ "Air Filter", 62.95) parts(54) = New PartDescription(990659, 2000, "Toyota", _ "RAV4 2WD/4-DOOR", "Cooling System", _ "Radiator OE Plastic tank", 136.85) parts(55) = New PartDescription(440574, 2007, "Buick", _ "Lacrosse CXS V6 3.6", "Suspension", _ "Strut Mount Inc; Sleeve; Rear Left", _ 80.8) ' Showing the makes nodes ' Showing the makes nodes For Each nodYear As TreeNode In nodRoot.Nodes Dim lstMakes As ArrayList = New ArrayList() For Each part As PartDescription In parts If nodYear.Text = part.CarYear.ToString() Then If Not lstMakes.Contains(part.Make) Then lstMakes.Add(part.Make) End If End If Next For Each strMake As String In lstMakes nodYear.Nodes.Add(strMake) Next Next ' Showing the models nodes For Each nodYear As TreeNode In nodRoot.Nodes For Each nodMake As TreeNode In nodYear.Nodes Dim lstModels As ArrayList = New ArrayList() For Each part As PartDescription In parts If nodYear.Text = part.CarYear.ToString() And _ (nodMake.Text = part.Make) Then If Not lstModels.Contains(part.Model) Then lstModels.Add(part.Model) End If End If Next For Each strModel As String In lstModels nodMake.Nodes.Add(strModel) Next Next Next ' Showing the categories nodes For Each nodYear As TreeNode In nodRoot.Nodes For Each nodMake As TreeNode In nodYear.Nodes For Each nodModel As TreeNode In nodMake.Nodes Dim lstCategories As ArrayList = New ArrayList() For Each part As PartDescription In parts If (nodYear.Text = part.CarYear.ToString()) And _ (nodMake.Text = part.Make) And _ (nodModel.Text = part.Model) Then If Not lstCategories.Contains(part.Category) Then lstCategories.Add(part.Category) End If End If Next For Each strCategory As String In lstCategories nodModel.Nodes.Add(strCategory) Next Next Next Next End Sub

2. Save the file

The number of nodes in the TreeNode objects is stored in the TreeNodeCollection.Count property. To get the current number of nodes in the tree view, you can call the TreeView.GetNodeCount() method. Its syntax is:

Public Function GetNodeCount(includeSubTrees As Boolean) As Integer

Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            . . . No Change

            Controls.Add(tvwCountries)

            Dim NodeCount As Integer = tvwCountries.GetNodeCount(True)
            Text = CStr(NodeCount)
End Sub

This would produce:

If you create a node and add it to a branch that already contains another node, the new node is referred to as a sibling to the existing child node.

In our introduction, we saw that a node, any node, could have as many nodes as you judge necessary. To support this, the TreeNode class is equipped with a property called Nodes, which, like that of the TreeView class, is based on the TreeNodeCollection class. This allows you to refer to the list of children of the node that this Nodes property belongs to. With this information, you can further create or manipulate child nodes of any node as you wish.

Besides looking at a node, probably the primary action a user performs on a tree is to select an item. To select a node in the tree, the user can click it. To programmatically select a node, assign its reference to the TreeView.SelectedNode property. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodAfrica As TreeNode = New TreeNode("Africa")
            Dim nodAmerica As TreeNode = New TreeNode("America")
            Dim nodEurope As TreeNode = New TreeNode("Europe")
            Dim nodContinents() As TreeNode = {nodAfrica, nodAmerica, nodEurope}

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            tvwCountries.SelectedNode = nodAmerica

            Controls.Add(tvwCountries)
End Sub

After selecting a node, the tree view indicates the item selected by highlighting it. In the following picture, the America node is selected:

To programmatically find out what item is selected in the tree, get the value of the TreeView.SelectedNode Boolean property. If no node is selected, this property produces null. Alternatively, you can check the value of a node's TreeNode.IsSelected Boolean property to find out if it is currently selected.

After locating a node, the user may want to change its text. To change the string of a node, it must be put to edit mode. To do this, you can call the TreeNode.BeginEdit() method. Its syntax is:

Public Sub BeginEdit

When a node is in edit mode, the caret blinks in its edit box section. The user can then type a new string or edit the existing string. After setting the (new) string, the user can press Enter or may click somewhere. At this time, you need to indicate that the user has finished this operation. To do this, you can call the TreeNode.EndEdit() method. Its syntax is:

Public Sub EndEdit(cancel As Boolean)

Just before this method, you can check the content of the string that was added or edited. This allows you to accept or reject the change. The argument to the EndEdit() method allows you to validate or cancel the editing action.

As mentioned already, the nodes of a tree view are stored in a collection of type TreeNodeCollection. Every time you create a new node, it occupies a position inside the tree. Each node is represented by the Item indexed property of this collection. The first node of the tree has an index of 0.

When you call the TreeNodeCollection.Add() method to create a node, the new branch is added at the end of the list of its siblings. If you want, you can add a new child somewhere in the tree. To do this, you would call the TreeNodeCollection.Insert() method. Its syntax is:

Public Overridable Sub Insert(index As Integer, node As TreeNode)

The first argument to this method is the index that the new node will occupy when created. The second argument is a reference to the new node to be created. Here is an example of using it:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = _
                   { _
                       New TreeNode("Africa"), _
                       New TreeNode("America"), _
                       New TreeNode("Asia"), _
                       New TreeNode("Europe") _
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            tvwCountries.Nodes.Insert(1, New TreeNode("Neptune"))
            Controls.Add(tvwCountries)
End Sub

This would produce:

Another technique you can use to locate a node consists of using some coordinates. To do this, you can call the TreeView.GetNodeAt() method that is overloaded with two versions whose syntaxes are:

Public Function GetNodeAt(x As Integer, y As Integer) As TreeNode
Public Function GetNodeAt(pt As Point) As TreeNode

To use this method, you must know either the Point location or the x and y coordinates of the node. If you provide valid arguments to this method, it returns a reference to the TreeNode located at the argument. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = _
                   { _
                       New TreeNode("Africa"), _
                       New TreeNode("America"), _
                       New TreeNode("Asia"), _
                       New TreeNode("Europe") _
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            tvwCountries.ExpandAll()
            Dim nodBranch As TreeNode = tvwCountries.GetNodeAt(22, 48)

            Controls.Add(tvwCountries)
            Text = nodBranch.Text
End Sub

This would produce:

After creating a tree, to get a reference to the first child node, you can retrieve the TreeNode.FirstNode property. You would use code as follows:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = _
                   { _
                       New TreeNode("Africa"), _
                       New TreeNode("America"), _
                       New TreeNode("Asia"), _
                       New TreeNode("Europe") _
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            dim nodFirst  as  TreeNode = tvwCountries.Nodes(0).FirstNode

            Controls.Add(tvwCountries)
            Text = nodFirst.Text
End Sub

To get a reference to the last child node, retrieve the TreeNode.LastNode property. You would use code as follows:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            Dim nodContinents() As TreeNode = _
                   { _
                       New TreeNode("Africa"), _
                       New TreeNode("America"), _
                       New TreeNode("Asia"), _
                       New TreeNode("Europe") _
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)

            Dim nodLast As TreeNode = tvwCountries.Nodes(0).FirstNode

            Controls.Add(tvwCountries)
            Text = nodLast.Text
End Sub

To get a reference to the sibling above a node, if any, you can retrieve its TreeNode.PrevNode property. To get a reference to the sibling below a node, if any, you can retrieve its TreeNode.NextNode property.

To find whether a tree view contains a certain node, you can call the TreeNodeCollection.Contains() method. Its syntax is:

Public Function Contains(node As TreeNode) As Boolean

This method expects as argument a reference to the node to look for. If the tree contains that node, the method returns true. If the node is not found, this method returns false.

1. In the Class Name combo box, select tvwAutoParts
2. In the Method Name combo box, select NodeMouseClick
3. Implement the event as follows:
    

   Private Sub tvwAutoParts_NodeMouseClick(ByVal sender As Object, _ ByVal e As System.Windows.Forms.TreeNodeMouseClickEventArgs) _ Handles tvwAutoParts.NodeMouseClick Dim nodClicked As TreeNode = e.Node If nodClicked.Level = 4 Then lvwAutoParts.Items.Clear() Try Try For Each part As PartDescription In parts If (part.Category = nodClicked.Text) And _ (part.Model = nodClicked.Parent.Text) And _ (part.Make = nodClicked.Parent.Parent.Text) And _ (part.CarYear.ToString() = nodClicked.Parent.Parent.Parent.Text) Then Dim lviAutoPart As ListViewItem = New ListViewItem(part.PartNumber.ToString()) lviAutoPart.SubItems.Add(part.PartName) lviAutoPart.SubItems.Add(part.UnitPrice.ToString()) lvwAutoParts.Items.Add(lviAutoPart) End If Next Catch ex As NullReferenceException End Try Catch ex As NullReferenceException End Try End Sub

4. Under the above End Sub line, create the following procedure:
    

   Private Sub CalculateOrder() ' Calculate the current total order and update the order Dim SubTotal1 As Double Dim SubTotal2 As Double Dim SubTotal3 As Double Dim SubTotal4 As Double Dim SubTotal5 As Double Dim SubTotal6 As Double Dim OrderTotal As Double ' Retrieve the value of each sub total Try SubTotal1 = CDbl(txtSubTotal1.Text) Catch MsgBox("Invalid Value") End Try Try SubTotal2 = CDbl(txtSubTotal2.Text) Catch MsgBox("Invalid Value") End Try Try SubTotal3 = CDbl(txtSubTotal3.Text) Catch MsgBox("Invalid Value") End Try Try SubTotal4 = CDbl(txtSubTotal4.Text) Catch MsgBox("Invalid Value") End Try Try SubTotal5 = CDbl(txtSubTotal5.Text) Catch MsgBox("Invalid Value") End Try Try SubTotal6 = CDbl(txtSubTotal6.Text) Catch MsgBox("Invalid Value") End Try ' Calculate the total value of the sub totals OrderTotal = SubTotal1 + SubTotal2 + SubTotal3 + _ SubTotal4 + SubTotal5 + SubTotal6 ' Display the total order in the appropriate text box txtTotalOrder.Text = CStr(OrderTotal) End Sub

5. In the Class Name combo box, select lvwAutoParts
6. In the Method Name combo box, select DoubleClick and implement the event as follows:
    

   Private Sub lvwAutoParts_DoubleClick(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles lvwAutoParts.DoubleClick Dim lviAutoPart As ListViewItem = lvwAutoParts.SelectedItems(0) If lvwAutoParts.SelectedItems.Count = 0 Or _ lvwAutoParts.SelectedItems.Count > 1 Then End If If txtPartNumber1.Text = "" Then txtPartNumber1.Text = lviAutoPart.Text txtPartName1.Text = lviAutoPart.SubItems(1).Text txtUnitPrice1.Text = lviAutoPart.SubItems(2).Text txtQuantity1.Text = "1" txtSubTotal1.Text = lviAutoPart.SubItems(2).Text txtQuantity1.Focus() ' If the previous Part # text box is not empty, then use the next one ElseIf txtPartNumber2.Text = "" Then txtPartNumber2.Text = lviAutoPart.Text txtPartName2.Text = lviAutoPart.SubItems(1).Text txtUnitPrice2.Text = lviAutoPart.SubItems(2).Text txtQuantity2.Text = "1" txtSubTotal2.Text = txtUnitPrice2.Text txtQuantity2.Focus() ElseIf txtPartNumber3.Text = "" Then txtPartNumber3.Text = lviAutoPart.Text txtPartName3.Text = lviAutoPart.SubItems(1).Text txtUnitPrice3.Text = lviAutoPart.SubItems(2).Text txtQuantity3.Text = "1" txtSubTotal3.Text = txtUnitPrice3.Text txtQuantity3.Focus() ElseIf txtPartNumber4.Text = "" Then txtPartNumber4.Text = lviAutoPart.Text txtPartName4.Text = lviAutoPart.SubItems(1).Text txtUnitPrice4.Text = lviAutoPart.SubItems(2).Text txtQuantity4.Text = "1" txtSubTotal4.Text = txtUnitPrice4.Text txtQuantity4.Focus() ElseIf txtPartNumber5.Text = "" Then txtPartNumber5.Text = lviAutoPart.Text txtPartName5.Text = lviAutoPart.SubItems(1).Text txtUnitPrice5.Text = lviAutoPart.SubItems(2).Text txtQuantity5.Text = "1" txtSubTotal5.Text = txtUnitPrice5.Text txtQuantity5.Focus() ElseIf txtPartNumber6.Text = "" Then txtPartNumber6.Text = lviAutoPart.Text txtPartName6.Text = lviAutoPart.SubItems(1).Text txtUnitPrice6.Text = lviAutoPart.SubItems(2).Text txtQuantity6.Text = "1" txtSubTotal6.Text = txtUnitPrice6.Text txtQuantity6.Focus() ' If all Part # text boxes are filled, don't do anything Else Exit Sub End If CalculateOrder() End Sub

7. In the Class Name combo box, select txtQuantity1
8. In the Method Name combo box, select Leave and implement the event as follows:
    

   Private Sub txtQuantity1_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtQuantity1.Leave Dim Quantity As Integer Dim UnitPrice As Double, SubTotal As Double ' Get the quantity of the current item Try Quantity = CInt(txtQuantity1.Text) Catch MsgBox("Invalid Value") End Try ' Get the unit price of the current item Try UnitPrice = CDbl(txtUnitPrice1.Text) Catch MsgBox("Invalid Value") End Try ' Calculate the current sub total SubTotal = Quantity * UnitPrice ' Display the new sub total in the corresponding text box txtSubTotal1.Text = SubTotal.ToString() ' Update the order CalculateOrder() End Sub

9. In the Class Name combo box, select txtQuantity2
10. In the Method Name combo box, select Leave and implement the event as follows:
     

    Private Sub txtQuantity2_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtQuantity2.Leave Dim Quantity As Integer Dim UnitPrice As Double, SubTotal As Double Try Quantity = CInt(txtQuantity2.Text) Catch MsgBox("Invalid Value") End Try Try UnitPrice = CDbl(txtUnitPrice2.Text) Catch MsgBox("Invalid Value") End Try SubTotal = Quantity * UnitPrice txtSubTotal2.Text = SubTotal.ToString() CalculateOrder() End Sub

11. In the Class Name combo box, select txtQuantity3
12. In the Method Name combo box, select Leave and implement the event as follows:
     

    Private Sub txtQuantity3_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtQuantity3.Leave Dim Quantity As Integer Dim UnitPrice As Double, SubTotal As Double Try Quantity = CInt(txtQuantity3.Text) Catch MsgBox("Invalid Value") End Try Try UnitPrice = CDbl(txtUnitPrice3.Text) Catch MsgBox("Invalid Value") End Try SubTotal = Quantity * UnitPrice txtSubTotal3.Text = SubTotal.ToString() CalculateOrder() End Sub

13. In the Class Name combo box, select txtQuantity4
14. In the Method Name combo box, select Leave and implement the event as follows:
     

    Private Sub txtQuantity4_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtQuantity4.Leave Dim Quantity As Integer Dim UnitPrice As Double, SubTotal As Double Try Quantity = CInt(txtQuantity4.Text) Catch MsgBox("Invalid Value") End Try Try UnitPrice = CDbl(txtUnitPrice4.Text) Catch MsgBox("Invalid Value") End Try SubTotal = Quantity * UnitPrice txtSubTotal4.Text = SubTotal.ToString() CalculateOrder() End Sub

15. In the Class Name combo box, select txtQuantity5
16. In the Method Name combo box, select Leave and implement the event as follows:
     

    Private Sub txtQuantity5_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtQuantity5.Leave Dim Quantity As Integer Dim UnitPrice As Double, SubTotal As Double Try Quantity = CInt(txtQuantity5.Text) Catch MsgBox("Invalid Value") End Try Try UnitPrice = CDbl(txtUnitPrice5.Text) Catch MsgBox("Invalid Value") End Try SubTotal = Quantity * UnitPrice txtSubTotal5.Text = SubTotal.ToString() CalculateOrder() End Sub

17. In the Class Name combo box, select txtQuantity6
18. In the Method Name combo box, select Leave and implement the event as follows:
     

    Private Sub txtQuantity6_Leave(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles txtQuantity6.Leave Dim Quantity As Integer Dim UnitPrice As Double, SubTotal As Double Try Quantity = CInt(txtQuantity6.Text) Catch MsgBox("Invalid Value") End Try Try UnitPrice = CDbl(txtUnitPrice6.Text) Catch MsgBox("Invalid Value") End Try SubTotal = Quantity * UnitPrice txtSubTotal6.Text = SubTotal.ToString() CalculateOrder() End Sub

19. In the Class Name combo box, select btnRemove1
20. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnRemove1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnRemove1.Click txtPartNumber1.Text = "" txtPartName1.Text = "" txtUnitPrice1.Text = "0.00" txtQuantity1.Text = "0" txtSubTotal1.Text = "0.00" CalculateOrder() End Sub

21. In the Class Name combo box, select btnRemove2
22. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnRemove2_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnRemove2.Click txtPartNumber2.Text = "" txtPartName2.Text = "" txtUnitPrice2.Text = "0.00" txtQuantity2.Text = "0" txtSubTotal2.Text = "0.00" CalculateOrder() End Sub

23. In the Class Name combo box, select btnRemove3
24. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnRemove3_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnRemove3.Click txtPartNumber3.Text = "" txtPartName3.Text = "" txtUnitPrice3.Text = "0.00" txtQuantity3.Text = "0" txtSubTotal3.Text = "0.00" CalculateOrder() End Sub

25. In the Class Name combo box, select btnRemove4
26. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnRemove4_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnRemove4.Click txtPartNumber4.Text = "" txtPartName4.Text = "" txtUnitPrice4.Text = "0.00" txtQuantity4.Text = "0" txtSubTotal4.Text = "0.00" CalculateOrder() End Sub

27. In the Class Name combo box, select btnRemove5
28. Double-click the fifth Remove button and implement its event as follows:
     

    Private Sub btnRemove5_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnRemove5.Click txtPartNumber5.Text = "" txtPartName5.Text = "" txtUnitPrice5.Text = "0.00" txtQuantity5.Text = "0" txtSubTotal5.Text = "0.00" CalculateOrder() End Sub

29. In the Class Name combo box, select btnRemove6
30. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnRemove6_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnRemove6.Click txtPartNumber6.Text = "" txtPartName6.Text = "" txtUnitPrice6.Text = "0.00" txtQuantity6.Text = "0" txtSubTotal6.Text = "0.00" CalculateOrder() End Sub

31. In the Class Name combo box, select btnClose
32. In the Method Name combo box, select Click and implement the event as follows:
     

    Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click End End Sub

33. Execute the application to test it
     
    
34. After using it, close the form

When a tree contains a few nodes, the user may want to delete some of them, for any reason. To delete a node, you can call the TreeNodeCollection.Remove() method. Its syntax is:

Public Sub Remove(node As TreeNode)

This method expects a reference to the node you want to delete. Another solution you can use would consist of locating the node by its index. To do this, you would call the TreeNodeCollection.RemoveAt() method. Its syntax is:

Public Overridable Sub RemoveAt(index As Integer)

When calling this method, pass the index of the node to be deleted. If you are already at that node and you want to remove it, you can call the TreeNode.Remove() method. Its syntax is:

Public Sub Remove

One of the characteristics of a tree in the real world is that, if you cut a branch, the branches attached to it and their leaves are cut too. In the same way, if you call any of these Remove() or RemoveAt() methods to delete a node, its children, if any, would be deleted too.

To remove all nodes of a tree view, you can call the TreeNodeCollection.Clear() method. Its syntax is:

Public Overridable Sub Clear

This method is used to get rid of all nodes of a tree.

After a node has been added to a tree, it holds a position relative to its parent and its existence depends on that parent. To keep track of its "ancestry", each node has a path that can be used to identify its parent and its grand-parent(s), if any. To know the path of a node from itself to the root, you can access its TreeNode.FullPath property. This property produces a string made of sections separated by a specific character identified as the TreeView.PathSeparator property. By default, this character is the backslash, following the conventions of the operating system. If you want to use a different character or string, assign it to the PathSeparator property. To know what character or string a tree view is using as the separator, you can retrieve the value of its PathSeparator property.

In order to select an item, the user must click it or navigate to it using the keyboard. Alternatively, if you want the items to be underlined when the mouse passes over them, set to true the TreeView.HotTracking Boolean property. Its default value is false. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.HotTracking = True

            Controls.Add(tvwCountries)

            Dim nodContinents() As TreeNode = _
                   { _
                       New TreeNode("Africa"), _
                       New TreeNode("America"), _
                       New TreeNode("Asia"), _
                       New TreeNode("Europe") _
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)
End Sub

This would produce:

As mentioned already, a tree view appears as a list of items arranged like a tree. This implies a relationship of parent-child among the items in the control. To indicate this relationship between two nodes, a line is drawn from one to another. Based on this, a line from a node on top of another node under it indicates that the one on top is the parent to the one under it.

The presence or absence of the lines among related nodes is controlled by the TreeView.ShowLines Boolean property. By default, this property is set to true (in the .NET Framework, some other libraries have it set by default to false). If this property is set to false, the lines between the nodes would not display. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.ShowLines = False

            Controls.Add(tvwCountries)

            Dim nodContinents() As TreeNode = _
                   { _
                       New TreeNode("Africa"), _
                       New TreeNode("America"), _
                       New TreeNode("Asia"), _
                       New TreeNode("Europe") _
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)
End Sub

This would produce:

If you create a tree that has more than one root, a line is drawn among those root nodes. Here is an example:

The presence or absence of this type of line is controlled by the TreeView.ShowRootLines Boolean property.

Indentation is the ability for a child node to be aligned to the right with regards to its parent. The general distance from the left border of the parent to the left border of the child is partially controlled by the TreeView.Indent property which is an integer. If the default distance doesn't suit you, you can change it by assigning a positive number to the control's Indent property.

When the user clicks an item, that node becomes highlighted for the length of its string. If you want, you can show the highlighting on the selected node but from the left to the right borders of the tree view. To do this, you can set the TreeView.FullRowSelect Boolean property to true. Its default value is false. For the TreeView.FullRowSelect property to work, the ShowLines property must be set to false. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.HotTracking = True
            tvwCountries.ShowLines = False
            tvwCountries.FullRowSelect = True

            Controls.Add(tvwCountries)

            Dim nodContinents() As TreeNode = _
                   { _
                       New TreeNode("Africa"), _
                       New TreeNode("America"), _
                       New TreeNode("Asia"), _
                       New TreeNode("Europe") _
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)
End Sub

This would produce:

We saw that, to select an item, the user can click it. If the user clicks another control, the node that was selected in the tree view loses its highlighting because the control has lost focus. When the focus moves to another control, if you want the selected node of the tree view to preserve its highlighting, set to false the TreeView.HideSelection Boolean property. Its default value is true.

At this time, we have seen that some nodes have children and some don't. When a node has at least one child, the node indicates this by displaying a + button. If the user clicks the + button, the node expands, displays a list of its children, and the button becomes -. The presence or absence of the + and - buttons is controlled by the TreeView.ShowPlusMinus Boolean property. By default, this property is set to true. If you don't want the parent nodes to display the + or - button, set this property to false.

When a node displays a + button and the user clicks that button, the node displays its child(ren). This action is referred to as expanding the node. To programmatically expand a node, call its TreeNode.Expand() method. Its syntax is:

Public Sub Expand

This method only expands the node that calls it but if its children have their own children, they are not expanded.  To expand a node and its children that have nodes, you can call its TreeNode.ExpandAll() method. Its syntax is:

Public Sub ExpandAll

To find out if a node is expanded, check the value of its TreeNode.IsExpanded property.

To expand other nodes of the tree view, the user can continue clicking each node that has a + button as necessary. To programmatically expand all nodes of a tree view, call its TreeView.ExpandAll() method. Its syntax is:

Public Sub ExpandAll

If a node is displaying a - button, it indicates that it is showing the list of its children. To hide the list, the user can click the - button. This action is referred to as collapsing the node. To programmatically collapse a node, call its TreeNode.Collapse() method whose syntax is:

Public Sub ExpandAll

The user can do this for each node that is expanded. To programmatically collapse all nodes of a tree view, call its TreeView.CollapseAll() method. Its syntax is:

Public Sub CollapseAll

Besides the strings (and some small pictures as we will see later), the nodes of a tree view can display a check box on their left side. The presence or absence of the check box is controlled by the CheckBoxes Boolean property whose default value is false. If you want to display the check boxes, set this property to true. Here is an example:

Public Sub InitializeComponent()
            Text = "Countries Statistics"
            Size = New Size(242, 280)

            tvwCountries = New TreeView()

            tvwCountries.Location = New Point(12, 12)
            tvwCountries.Width = 210
            tvwCountries.Height = 230

            tvwCountries.CheckBoxes = True

            Controls.Add(tvwCountries)

            Dim nodContinents() As TreeNode = _
                   { _
                       New TreeNode("Africa"), _
                       New TreeNode("America"), _
                       New TreeNode("Asia"), _
                       New TreeNode("Europe") _
                   }

            Dim nodWorld As TreeNode = New TreeNode("World", nodContinents)
            tvwCountries.Nodes.Add(nodWorld)
End Sub

This would produce:

If you equip the nodes with check boxes, the user can click an item to select it independently of the check box. The user can also click the check box, which would place a check mark in the box. To programmatically check the box, you can assign a true value to the node's Checked property.

When a check mark has been placed in a node's check box, the tree view fires an AfterCheck event, which is handled by the TreeViewEventHandler delegate. The AfterCheck event is carried by the TreeViewEventArgs class. One of properties of this class is called Action, which specifies why or how the event occurred. The Action property is in fact a value based on the TreeViewAction enumerator. Its members are:

ByKeyboard: This indicates that the event was fired by pressing a key

ByMouse: This indicates that the event was fired based on an action on the mouse

Collapse: This indicates that event was fired when the tree collapsed

Expand: This indicates that the event was fired when the tree expanded

Unknown: None of the above reasons caused the event, but the event was fired

The other property of the TreeViewEventArgs class is called Node. This member is of type TreeNode. It carries a reference to the node that fired the event, whether it was clicked, checked, expanded, or collapsed.

To programmatically find out if a node is checked, check the value of its Checked property.

Each of the nodes we have used so far displayed a simple piece of text. To enhance the appearance of a node, besides its text, you can display a small icon to the left of its string. To do this, you must first create an ImageList control and assign it to the TreeView.ImageList property.

When creating a node, if you plan to display an icon next to it, you can use the following constructor of the TreeNode class:

Public Sub New ( _
	text As String, _
	imageIndex As Integer, _
	selectedImageIndex As Integer _
)

This constructor allows you to specify the text that the node will display, the index of the picture it will use in the ImageList property, and the picture it will display when it is selected.

If you are creating a node with its children and you want to specify its pictures, use the following constructor of the TreeNode class:

Public Sub New ( _
	text As String, _
	imageIndex As Integer, _
	selectedImageIndex As Integer, _
	children As TreeNode() _
)

Just as done previously, after defining the TreeNode object, you can add it to the tree by passing it to the TreeNodeCollection.Add() method. In the same way, you can create an array of TreeNode objects and pass it to the TreeNodeCollection.AddRange() method.

Practical Learning: Associating Icons With Nodes